It goes almost without saying that messaging systems need an easy-to-use means of notifying subscribers that unanswered or high priority messages are waiting. The notification paradigm should fit subscribers' convenience and habitual activity patterns. Otherwise, subscribers must constantly interrupt their activities to access their message "mailboxes" without knowing in advance that there are messages actually waiting. When subscribers are far from home, they have to make expensive telephone calls just to find out whether they have any messages waiting. When at home, telephone answering machines typically provide visual indicator lights which are convenient and easy to use, but the customer must be physically present at the location to make use of them. Network voice mailbox services can likewise provide visual indicators (call waiting lights), but these are typically built into special terminal equipment. The network mailbox services can provide audio indicators such as "stutter dial tone", but subscribers must develop the habit of picking up the phone specifically to hear the notification. Many subscribers do not understand the meaning of the special tone, and only phones on a common line connected to the message service receive the notification.
These problems will become more serious as subscribers use messaging services more widely. Subscribers increasingly have multiple e-mail and/or voice accounts (e.g., at work and home), Internet chat and mail, multiple phone lines in the home with messaging capability, Internet voice telephony and messaging, etc. Regularly checking all these sources for messages can become tedious.
Ideally, there should be a single point of notification for all waiting messages, and for multiple mailboxes within each medium, if present. No such arrangements exist today.